Location: This prospect is on the crest of hill 206, locally called Gold Hill, on the west side of Snake River between its tributaries Monument and Thompson Creeks. The map location is near the center of section 21, T. 10 S., R. 34 W., Kateel River Meridian. It is locality 44 of Cobb (1972 [MF 463], 1978 [OFR 78-93]).
Geology: The Gold Hill prospect is on a low bedrock hill tht is thinly covered by soil. Several subdued and sloughed prospect pits are near the crest of the hill, and another pit is on the southeast flank of the hill just above Snake River. Cathcart (1922, p. 247) described the deposits as thin quartz-feldspar veins and weathered sulfidized zones that panned free gold. In 1990, Kennecott Exploration Company completed a soil geochemical survey over Gold Hill. The survey consisted of six north-trending lines 400 feet apart, along which soil samples were collected on 200-foot centers. The survey revealed extensive zones of high arsenic, moderate gold, and weak antimony geochemical anomalies. The soil survey was followed up by about 3,200 feet of roughly north-south trenching and by two diamond core holes, each about 350 feet deep (C.C. Hawley and Cindy Buxton, written communication, 1992). The trenching indicated that Gold Hill was crossed by about six lenticular east-northeast-trending mineralized zones as much as 80 feet wide. The best zone in the northern half of the easternmost trench contained 80 feet of material that assayed 280 to 2,540 ppb gold and 3,560 to more than 10,000 ppm arsenic. This zone is marked by sparse quartz boulders containing minor disseminated galena and by old prospect pits. The highest antimony values, 150 to 250 ppm, were in parts of the trench system having lower gold and arsenic values. Drill samples showed substantially lower values than those in samples from the trenches, suggesting that gold was enriched near the surface. The upper 50 feet of core hole GHDH-2 penetrated about 40 feet of rock averaging 0.01 ounce of gold per ton and 5 feet of rock containing 1,360 ppb gold. Core hole GHDH-1 penetrated nearly 80 feet of mineralized schist and quartz veins near the bottom of the hole but values were generally less than 100 ppb gold; the maximum value for a 3-foot mineralized zone within the 80-foot zone was 2,210 ppb Au.
Workings: Cathcart (1922) reported as much as about 0.17 ounce of gold per ton in narrow vein zones. Soil sampling, trenching, and drilling by Kennecott Exploration Co. in 1990 and 1991 found wide low-grade zones that appear to have been upgraded by secondary enrichment.
Age: Mid-Cretaceous or younger; postdates regional metamorphism of the host rocks.
Alteration: Sulfidation and silicification.

Commodities (Major) - Ag, Au; (Minor) - Sb
Development Status: None
Deposit Model: Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a).

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Standard Detailed Gallery Strunz Chemical Elements

Commodity List

This is a list of exploitable or exploited mineral commodities recorded at this locality.

ⓘ Antimony

ⓘ Silver

Mineral List

6 valid minerals.